1. Field of the Invention
The present invention relates to an ink jet recording medium. More particularly, the present invention relates to an ink jet recording medium having an excellent ink absorption and a superior reproducibility of ink images with a high resolving power for the ink images.
2. Description of the Related Art
An ink jet recording system, in which an aqueous ink is jetted imagewise through a fine opening of a jetting nozzle toward a recording material to form ink images, is advantageous in that printing noise is low, full colored images can be easily recorded, the recording can be effected at a high speed, and the ink jet printer is cheaper than other printers, and thus the application of the ink jet recording system has progressed in many fields including, for example, terminal printers for computers, facsimile machines, plotters, and book and slip printers.
Generally, conventional woodfree paper sheets and coated paper sheets exhibit a poor ink absorption and thus the ink images printed of the above-mentioned paper sheets are retained in an undried condition for a long time and thus cause the printing apparatus, printed sheets and the printed ink images to be stained by the undried ink images. Thus, the conventional woodfree paper sheets and coated paper sheets are not practically useful for the ink jet printing. To solve these problems, Japanese Unexamined Patent Publication No. 52-53,012 discloses an ink jet recording paper sheet having a low degree of sizing, and Japanese Unexamined Patent Publication No. 53-49,113 discloses an ink jet recording sheet produced by impregnating a paper sheet containing an internally added urea-formaldehyde resin with a water soluble polymeric material. Also, Japanese Unexamined Patent Publications No. 55-51583 and No. 56-148,585 disclose an ink jet recording sheet having a coating layer formed on a substrate paper sheet and comprising a certain type of porous inorganic pigment particles, for example, amorphous silica particles, for the purpose of enhancing the color density and the reproducibility of the printed ink images.
Further, for the purpose of obtaining ink images having a high sharpness with a high resolution while preventing or restricting blotting of ink, Japanese Unexamined Patent Publications No. 58-110,287, No. 59-185,690 and No. 61-141,584 respectively disclose an improvement of the physical properties of the porous pigment particles. The improved porous pigment particles contribute to enhancing the recording properties of the recording sheet to a certain extent.
Currently, ink jet printing technology has been significantly advanced, and in a recent technology, the resultant quality of the ink jet printed images is comparable to that of the silver salt photographic images. Thus, the demands on the quality of the ink jet recording media become stronger than before. Particularly, in ink jet recording printers using an ink having a low concentration of dye, which ink is referred to as a photo ink, there is a tendency that the photo ink is applied in an increased amount to the recording medium.
To cope with the tendency, the recording medium must have a high ink absorbing capacity.
The ink absorbing capacity of the recording medium can be increased by the following means.
(1) The ink receiving layer is formed in an increased amount.
(2) The content of a binder to be contained in the ink receiving layer is increased.
(3) In the ink receiving layer, pigment particles having an increased pore volume are contained.
(4) In the ink receiving layer, pigment particles having a decreased range of distribution in the particle size are contained.
(5) The degree of sizing of the substrate paper sheet is decreased to cause the ink to easily permeate into the substrate paper sheet.
The means (1) is disadvantageous in that the resultant ink receiving layer exhibits a reduced surface strength, and thus a degraded pencil-writing property and the ink images recorded in the ink receiving layer exhibit a decreased color density.
The means (2) and (3) are disadvantageous in that the ink receiving layer exhibits a reduced surface strength and a degraded pencil-writing property.
Regarding means (4), it is difficult to find a pigment, for example a silica pigment, having a narrow range of pigment particle size distribution and capable of causing the ink images recorded in the ink receiving layer to have an increased color density and the ink receiving layer to exhibit an enhanced pencil-writing property.
The means (5) is disadvantageous in that the resultant substrate paper sheet exhibits a decreased resistance to penetration of a coating liquid for the ink receiving layer thereinto and as a result, the resultant ink receiving layer exhibits a reduced surface strength.
Further, when the ink-absorbing capacity is increased, the ink is rapidly absorbed in the resultant ink receiving layer while the ink applied to the ink receiving layer does not fully spread in the ink receiving layer, and thus the size of the resultant ink dots tends to become small. When the size of the ink dots is too small, the intervals between the ink dots become large and the color density of the resultant ink images is reduced.
An object of the present invention is to provide an ink jet recording medium having a sufficient ink absorbing capacity in practice and capable of recording thereon ink images having high color density, clarity and sharpness with a high resolution.
Another object of the present invention is to provide an ink jet recording medium capable of recording thereon ink images having high clarity and sharpness with a high reproducibility, sufficient surface strength as an office recording sheet, a good pencil-writing property and a good erasing property, for pencil marks, using an erasing rubber.
The above-mentioned objects can be attained by the ink jet recording medium of the present invention.
The ink jet recording medium of the present invention comprises a support material and at least one ink receiving layer formed on the support material and comprising xerogel porous pigment particles,
wherein a plurality of ink dots, each of which dots are formed by jetting three coloring ink droplets different in color from each other and equal in droplet volume to each other, toward a point of the ink receiving layer, to form a dot having a mixed color produced from the three coloring ink droplets superposed on each other at the point of the ink receiving layer, have an average dot size of 125% or less, based on an average size of ink dots, each of which dots are formed by jetting a droplet of each of the three different coloring inks having a droplet volume equal to that of each of the above-mentioned three coloring ink droplets, toward a point of the ink receiving layer, to form a dot having a single color of each ink.
In the ink jet recording medium of the present invention, the average dot size of the dots each formed from the three coloring ink droplets is preferably 110% or less, based on the average size of dots each formed by jetting two of the three coloring ink droplets toward a point of the ink receiving layer to form a dot having a mixed color of the two coloring ink droplets.
In the ink jet recording medium of the present invention, the xerogel porous pigment preferably comprises at least two types of amorphous silica particles different in specific surface area from each other, the highest specific surface area amorphous silica particles having a BET specific surface area of 300 to 900 m2/g and the lowest specific surface area amorphous silica particles having a BET specific surface area of 150 to 450 m2/g and less than that of the highest specific surface area amorphous silica particles.
The ink jet recording medium of the present invention preferably has a density of 0.70 to 0.90 g/cm3.
The ink jet recording medium of the present invention exhibits, when distilled water is brought into contact with the ink receiving layer, a distilled water-absorption of 30 g/m2 or more in a contact time of 10 ms determined by a dynamic scanning absorptometer.
In the method of recording colored images on the ink jet recording medium of the present invention using an ink jet recording machine and at least one member selected from the group consisting of yellow coloring inks, cyan coloring inks, magenta-coloring inks and black coloring inks, the ink can be applied in a maximum ink-applying amount of 20 ml/m2 or more, to the ink jet recording medium, by the recording machine.
The average dot size of the ink dots formed on the ink jet recording medium can be determined by using a trade available dot analizer (model: DA-5000, made by OJI KEISOKUKIKAI K.K.).